Some electronic devices can be used to enter data in documents displayed by the device. For example, a device can display a document provided by an electronic document file, such as a portable document format (“PDF”) file document or a word processing file document, that may include one or more text fields in which text can be entered. In particular, a user can select a particular field, and a provide text input information using an input interface of the device. Text corresponding to the text input information can be displayed in a text field of the document, and saved or printed as part of the document file. Some documents, however, must be signed by a user. For example, government-issued or legal documents can require a signature before being filed. When such documents are created or filled-in on an electronic device, a user may not have a simple mechanism for including a signature in the document. Instead, a user may be forced to print a physical hardcopy of the document, sign the printed document, and transmit the signed physical document to a receiving party (e.g., by mail, facsimile, or by scanning the signed physical document and e-mailing the scanned document). This approach can be time consuming and burdensome for a user.